1. Field of the Inventions
This invention relates to the field of vehicular air bag sensors which, when subjected to a deceleration force exceeding a preset limit, are operative to generate a signal to cause actuation of the air bag, and, more particularly to such an air bag sensor which is environmentally sealed from the operating environment of the vehicle.
2. Description of the Relevant Prior Art
In response to a perceived public desire for more safety features in passenger motor vehicles, and in compliance with federal regulations, many vehicles now being manufactured in the United States are equipped with driver's side air bags as standard or optional equipment. By 1995, driver's side air bags will be standard equipment on all passenger motor vehicles manufactured or sold in the United States. Furthermore, it is expected that such air bags will increasingly become available as options on the passenger side of the vehicle, as well.
Typical vehicular air bags remain in a compacted, deflated state until activated. When the vehicle is subjected to a sudden decelerating force, such as is caused by the impact of hitting another vehicle or a stationary object, the bag is quickly activated and inflates by rapid expansion of various gasses to create a deformable cushion between the driver and the interior of the vehicle, thereby preventing injury to the driver, or greatly diminishing the severity thereof.
The designer of an air bag safety system is faced with two competing requirements. First, the bag must inflate promptly, almost instantly, after impact. On the other hand, the air bag must not inflate inappropriately, as may happen if the vehicle is nudged or bumped in traffic or travels over uneven terrain or potholes. An accidental and inappropriate inflation of the air bag may actually lead to severe accidents because the driver can no longer operate the vehicle. In view of these competing requirements, it is critical that the air bag system include an accurate and reliable sensor which will reliably generate an activation signal when the deceleration force to which the vehicle is subjected equals or exceeds a preset level, but will not generate the activation signal if the deceleration force falls below that level.
To this end, typical air bag systems employ one or more sensors which incorporate ball and tube accelerometers. In such an accelerometer, a ball of a certain mass is normally held by a magnet disposed at one end of the accelerometer. When the device is subject to a decelerating force of sufficient magnitude, the ball will become dislodged from the magnet. If the deceleration force is sufficient to overcome the attraction exerted by the magnet, the ball will roll to the other end of a tube and cause bridging of a pair of electrical terminals disposed at that end of the accelerometer and thereby producing a detectable electrical characteristic which may be used to trigger airbag inflation.
Typically, a pair of these sensors are mounted on either side of the front bumper of the vehicle. A third sensor is mounted in the center of the vehicle, and somewhat further toward the rear thereof. The third sensor acts as an override to prevent accidental activation of the air bag if the bumper sensors are subjected to relatively minor, and localized deceleration. The three sensors are in electrical communication with a central processing unit which evaluates the signals therefrom and is programmed to generate an activation signal to the air bag's actuation mechanism in appropriate circumstances.
The prior art sensors described above are successful, for the most part, in generating an activation signal only in appropriate circumstances. However, they do suffer from certain disadvantages. Typically, the sensor including the ball and tube accelerometer is provided as a single component. Electrical leads are mounted to the terminals of the accelerometer and extend out of the sensor component. These trailing electrical leads cause problems during manufacture of the sensor component since various assembly steps may place undue strain on the delicate leads, causing breakage or detachment from the terminals. This causes failure in a certain number of the prior art components. Furthermore, the prior art sensor components are often not sealed from the operating environment in which they will be installed. Hence, water, brine, and various corrosive environmental contaminants may enter the sensor component and cause short circuits, or other damage to the delicate electrical connections. Obviously, failure of a prior art sensor component due to environmental contamination may prove disastrous in an accident situation.
In our co-pending patent application Ser. No. 07/637,790, now U.S. Pat. No. 5,072,334, the disclosure of which is incorporated herein by reference, we disclosed and claim modular, replaceable, environmentally sealed, plug-in electrical components. By disposing the mating terminals of these plug-in electrical components inside a sealed housing, the electrical connection between the pairs of terminals is protected from environmental degradation. We have found that the principle of encapsulating the terminal engagement inside a sealed housing may be adapted for constructing our novel environmentally sealed air bag sensor. While the internally mating terminals disclosed in Ser. No. 07/637,790, now U.S. Pat. No. 5,072,334 are disengageable to permit quick replacement of the various modular components, we have found it more expedient in the present case to utilize non-disengageable terminal connections in certain circumstances.